The present invention relates to a method for operating a hand-held transmitter for controlling vehicle functions, this hand-held transmitter being capable of emitting output signals for controlling both locking devices and drives for closing vehicle openings.
An infrared hand-held transmitter which is supplied for remote control of functions in vehicles manufactured by Mercedes-Benz is known. The output signals which can be emitted by this hand-held transmitter essentially comprise a code section and a maintenance section. Using the code section, a relatively short coded information item is transmitted in a known manner from the transmitter to a receiver fixed to the vehicle, which allows, for example, a central locking system to be activated in the sense of unlocking and locking, even at a relatively long range from the vehicle. The maintenance section, which also permits windows which are still open after leaving the vehicle and the sliding roof to be closed by means of their electrical drives in vehicles which are fitted with a convenience closing device, is emitted only and for as long as the transmitting key of the hand-held transmitter is held without interruption for longer than a predetermined time interval directly subsequent to the emission of the locking code signal, that is to say only for the desired duration of the window or sliding roof closing movement. For safety reasons, the closing movement does not begin until a specific time interval has elapsed, for example 0.25 seconds after the start, or after the receipt at the vehicle end, of the maintenance signal, in the same way as the necessary holding of the transmitting key already represents a safety measure.
In the simplest case, the maintenance section of output signals consists of repeated clock pulses which are transmitted at constant intervals at an intensity different from that of the code signal or with an unchanged signal level. The output power of the hand-held transmitter and its range thus remains the same (cf. FIG. 2).
In view of increased efforts relating to the operating reliability of vehicles, especially also those having such convenience closing systems, it is desirable to permit the operation of the systems by means of a remote control hand-held transmitter only within a relatively small spatial region around the vehicle.
The present invention achieves this by providing a method of operating a hand-held transmitter for controlling vehicle functions, in which the hand-held transmitter has the ability to emit output signals for controlling both locking devices and drives for closing vehicle openings. In this method, the hand-held transmitter emits the output signals for controlling locking devices at a first output power and range and emits the output signals for controlling the drives at a second output power and range. The second output power and range are lower than the first output power and range.
With the present invention, it is immaterial, for example, whether the output signal is activated in order to control the convenience closing drives, for example via a dedicated key on the hand-held transmitter, subsequent to a previous operation of a code signal transmitting key or whether only a single transmitting key is provided. In the first case, the output power which can be received is determined simply by the selection of the key.
A hand-held transmitter is known from German Patent Document DE 38 06 130 Al, whose output power is variable as a function of the intensity of the ambient lighting.
In an embodiment of the present invention, the output power which can be received from the hand-held transmitter, and hence its range, are automatically reduced during the sequence of the successive output signals which can be activated by a single conventional transmitting key.
In an embodiment of the present invention, the electrical output power of a signal source is reduced in one step by the upstream connection of a resistor, which forms an electrical filter.
In another embodiment of the invention, two signal sources are provided side-by-side in the same hand-held transmitter, one of which can emit at full power, unfiltered and unattenuated, the other of which can emit only through a filter which is always connected upstream, or at reduced power. In this embodiment, a changeover switch, which can be controlled automatically, for example as a function of time, is required in order to change over from the one signal source to the other in order to reduce the output power which can be received.
In another embodiment, two signal sources are implemented in that these sources are activated jointly for a large range and one of them is switched off to reduce the range.
Finally in another embodiment of the invention, a dialogue control of the output power which can be received from the hand-held transmitter is provided as a function of a long-range changeover signal which is emitted by the vehicle itself after complete reception of a matching code signal and can be received and evaluated in the hand-held transmitter.
If required, suitable, variable signal filtering is also provided, for example by switching on a suitable filter, which is selected depending on the type of signal carrier (infrared, ultrasound, radio), in front of the signal output during the emission of the output signals which control the drives.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.